Abstract

This is a review article on imaging findings in mediastinal pathology. Mediastinum is better studied on imaging methods such as plain radiography, MDCT, MRI and angiography.The characteristic findings of various mediastinal masses are described with a stress on plain radiography.Preoperative diagnosis can be made with imaging.

Key words:

Pediatrics, mediastinal masses, plain radiography.

Introduction

Mediastinum is a median septum or partition containing mass of tissues and organs between the two pleural sacs.Anteriorly the sternum,posteriorly vertebral column, superiorly thoracic inlet and inferiorly diaphragm constitute its borders. Heart is considered to be in the anterior mediastinum. Aortic arch, descending aorta and pulmonary vessels are in the middle mediastinum.These structures can be identified in poster anterior and lateral chest radiographs and abnormal masses can be studied123. CT and MRI may help to study the matrix as well as the capsule, thus, giving a histological diagnosis4. FNAC / biopsyare conducted to confirm the diagnosis.The imaging methods are in the following tableTable I: Plain radiography of the chest – PA and lateral, MD CTMRI, Angiography, Pet CT

In children, ALARA principle, (as low as reasonably allowable) should be adopted so that minimal radiation is used as the children are very sensitive to radiation exposures.Mediastinum is divided into various compartments (Figure 1ab).Felson[1]and other authors have divided the mediastinum into various compartments and Felson’s method is followed in this study2.

The following table lists the anterior mediastinal masses in children (Table II)

Table II: Enlarged thymus, Cystic Hygroma, Lymphoma, Teratodermoid

Thymomas are not generally encountered in children

In pediatric practice, most common mediastinal mass is the enlarged thymus.This may persist up to 4 years and rarely encountered even at 6-8 years[2]. Spontaneous regression is known and steroid therapy may help when the child is having respiratory problems (Figure 2ab).Radiologically, several signs have been described including the sail like density in the paratracheal area (Figure 3ab).

Figure 2ab :a- Persistent thymus, b-Post steroid therapy

Figure 3ab :a-Enlarged thymus, b-Sail like sign.

A wavy sign has been described where the costal cartilages produce an impression on the thymus (Figure 4ab-8abc).

CT imaging is performed to find out various sites of lymphadenopathy

Figure 10ab, Figure 11abcNext entity is sarcoidosis. Although,sarcoidosis is not very common in India and yet several cases have been reported in all ages[3]. Right paratracheal and bilateral hilar lymphadenopathy is characteristic. Unilateral hilar adenopathy may also be encountered[4].Figure 12

Figure 12 :16 yr old - Sarcoidosis with hilar lymphadenopathy .

Vascular rings and slings

These are often produce mediastinal widening simulating masses. Of these, right sided aorta with or without associated congenital heart disease is common. Although, plain films are classical as there is no normal aortic shadow on the left and an abnormal shadow is seen on right side of the trachea[5]. Normally, the trachea is deviated to the right by the presence of aortic knob. In right side aorta5, the trachea is deviated to the left (Figure 13a).

Figure 13a :Right sided aorta

Esophagogramconfirms the nature of the aorta. Angiogram is rarely necessary except when congenital heart disease is suspected (Figure 13bc).

Figure 13bc :Esophagogram with right sided aorta

Multidetector CT Angiogram is the latest investigation to be performed to study the cardiovascular structures (Figure 14ab)

Figure 14ab :a-Esophagogram, b-CT angiogram - Right sided aorta.

Next entity in the middle mediastinum comprises duplication cysts. Duplication cysts are congenital in nature and they may present as solid lesion on radiography (Figure 15ab)..

Figure 15ab :Esophgeal duplication cyst.

If they communicate with the respiratory / esophagus tract6. They may contain fluid / air[6]. CT often helps in identifying the nature of contents (Figure. 15c)

Figure 15c :CT showing fluid in the cyst.

Observe alarp principle as far as possible to avoid radiation exposure in children[7]. CT of the chest is often avoided and replaced by ultrasonography or magnetic resonance imaging. The indications are mentioned in table V

Table V - Indications for CT Chest

Table V:Identify mediastinal mass, To differentiate between solid and cystic lesions, To identify calcification, To identify fat, To study cardiovascular system

Most of the posterior Mediastinal masses are neurogenic and include the following:

Summary

Mediastinal Lesions in children are ideally studied by conventional radiographs. Where ever indicated advanced imaging methods are adopted. CT is minimally used to avoid excesive radiation. As far as possible ultrasonography and MRI studies should be replaced in the place of CT. Divisions of mediastinum help in identifying various masses.